swift - VideoComposition 不遵守指示

Question

自从更新到 iOS 13 以来，我用来淡入和淡出视频的视频合成已损坏。这是我的代码，在安装 iOS 13 之前一直可以正常工作。

现在，当我导出视频时，有声音，只是黑屏。

let urlAsset = AVURLAsset(url: inputURL, options: nil)      
guard let exportSession = AVAssetExportSession(asset: urlAsset, presetName: AVAssetExportPresetHighestQuality) else { handler(nil)
     return
}
exportSession.outputURL = outputURL
exportSession.outputFileType = AVFileType.m4v
exportSession.shouldOptimizeForNetworkUse = true

let composition = AVMutableVideoComposition(propertiesOf: urlAsset)

let clipVideoTrack = urlAsset.tracks(withMediaType: AVMediaType.video)[0]

let timeDuration = CMTimeMake(value: 1, timescale: 1)

let layer = AVMutableVideoCompositionLayerInstruction(assetTrack: clipVideoTrack)

// MARK: Fade in effect
layer.setOpacityRamp(fromStartOpacity: 0.0, toEndOpacity: 1.0, timeRange: CMTimeRange(start: CMTime.zero, duration: timeDuration))

// MARK: Fade out effect
let startTime = CMTimeSubtract(urlAsset.duration, CMTimeMake(value: 1, timescale: 1))

layer.setOpacityRamp(
       fromStartOpacity: 1.0,
       toEndOpacity: 0.0,
       timeRange: CMTimeRangeMake(start: startTime, duration: timeDuration)
)

let instruction = AVMutableVideoCompositionInstruction()
instruction.layerInstructions = [layer]
instruction.timeRange = CMTimeRange(start: CMTime.zero, duration: urlAsset.duration)


composition.instructions = [instruction]

exportSession.videoComposition = composition

exportSession.exportAsynchronously { () -> Void in
       handler(exportSession)
       print("composition has completed")
}

Answer 1

苹果公司表示存在一个错误，影响了一些合成指令。此问题已在 iOS 13.1 中修复。我更新并运行了该函数，淡入淡出效果与 iOS 13 更新之前一样。